Temperature dependence of the hydro-/dehydrogenation reaction kinetics on SmH ₂ films.

Abstract Rare-Earth and Mg-based metal hydrides undergo reversible changes in their optical, electrical, and thermal properties when absorbing or releasing hydrogen. These properties make them ideal for energy-efficient applications, such as hydrogen storage materials, switchable mirrors, and thermal switching devices. This study investigated the hydrogenation and dehydrogenation mechanisms of SmH 2 . The hydrogenation reaction of SmH 2 was successfully modeled using the JMAK model, which corresponds to the nucleation and growth mechanism of SmH 3 crystallites within the SmH 2 film. The Avrami exponent was extracted for each material to evaluate nucleation and growth behavior. Dehydrogenation was successfully evaluated using Fick’s second law, indicating that the dehydrogenation was dominated by diffusion. The activation energy of the SmH 2 hydrogenation reaction was approximately 140–180 kJ mol −1 , whereas that of the SmH 2 dehydrogenation reaction was about 60 kJ mol −1 . This indicates that the rate-determining step of the dehydrogenation process should be the recombination of hydrogen atoms on the Pd surface.